Generally, a harmonic driving device is a mechanical reduction mechanism, that is preferred comparing with the conventional gear transmission device by its compactness and light weight. Since the harmonic driving device can have wider transmission ratio range, i.e. the single-stage transmission ratio is ranged between 60˜320, and the multi-stage transmission ratio is ranged between 1600˜100000, it is further being preferred by its high transmission efficiency, high transmission precision and high bearing capacity and thus can be used in various industrial applications. It is noted that the harmonic driving device is commonly used in the field of high reduction ratio.
A conventional harmonic driving device is mainly composed of a wave generator, a flexible wheel and a rigid wheel. The wave generator is an oval-shaped device with a long axis and a short axis and is generally connected to a power input shaft. The flexible wheel is a flexible shallow cup with external gear that are positioned radially around the outside of the cup, and the cup is generally composed of a thin cylinder-shaped main body and a bottom that are integrally furnished, while being connected to a power output shaft by the bottom thereof. The rigid wheel is a rigid circular with internal gear on the inside. Operationally, the flexible wheel fits tightly over the wave generator, while allowing the flexible wheel to be placed inside the rigid wheel and enabling the external gear to mesh with the internal gear.
It is noted that the main body of the flexible wheel is designed with non-uniform thickness. As shown in FIG. 11, following the extending of the flexible wheel 90 from the external gear 93 to the bottom 92, the thickness of the main body 91 is tapered from the first thickness T1 to the second thickness T2. In an embodiment, when the first thickness T1 can be 0.4 mm, the tapering in thickness can reduce the second thickness T2 to 0.3 mm. However, as the harmonic driving device is designed to operate as a high-precision mechanical transmission shifting mechanism, such non-uniform thickness design can lead to high manufacture difficulty and poor production stability, and thus further adversely affect the power transmitted form the output shaft. Moreover, since the main body 91 of the flexible wheel 90 is furnished as a closed cup, its heat dissipation ability is poor and thus can cause its geometry to be deformed by the increasing temperature.
Therefore, it is important to have an improved harmonic driving device, which is designed for allowing its stiffness to be adjusted flexibly, and is able to eliminate vibration and noise while capable of solving the problem of uneven stress distribution on its flexible wheel.